Experience can shape the neural circuits in the brain. This experience-dependent neural plasticity is on the one hand critical for life, as employed for learning and memory, and is on the other hand noxious for life, which results in brain disorders. I will talk on two forms of neural plasticity that are induced by associative learning and nerve injury, respectively. First, I will talk on our findings from rats that revealed the existence of sensory-associated silent synapses in the CA1 hippocampus, which can be rapidly converted to functional synapses after associative fear learning and enable widespread excitatory responses in CA1 neurons to the newly memorized stimulus. Second, I will introduce a neural mechanism of synaptic plasticity that is responsible for nerve injury-induced disease, i.e, neuropathic (or chronic) pain, and will talk on a drug treatment with clinical potential to prevent this disease